1. (Field of the invention)
The present invention relates to a device which controls dropping at a desired speed of, for example, a medical liquid to be injected into a interior of a living body via 1 liquid sending set.
2. (Description of the prior art)
Medical liquid supported in a container is injected into the interior of a patient's body through a liquid sending set. and the dropping speed of the medical liquid must be controlled appropriately.
A manual roll clamp has been conveniently used as the dropping speed control. However, since the dropping speed is changed as a time passes and the roll has to be adjusted each time, a device which automatically controls the dropping speed has been recently distributed.
FIG. 8 is an outlined view showing a liquid sending control device now in use, where a container 100 holds the liquid, and a liquid carrying set 101 introduces the medical liquid into the interior of the patient's body. The liquid sending set 101 comprises a liquid needle 102 to be pierced into a mouth part of the container, a dropping tube 104, bendable tubes 103, 105 to be connected to the upper and lower parts of the dropping tube 104, and an injection needle (not shown) to be connected to the lower tube 105.
A liquid carrying control device 115 is composed of a dropping sensor 106 to be attached to the dropping tube 104 and a control device 107.
The control device 107 is, as shown in FIG. 9, formed with a tube holding groove 110 centrally in a vertical direction, and provided with a stationary clamp 108 and a movable clamp 109 in opposition to each other at a lower part of the tube holding groove 110.
A dropping number set switch 111 an electric source switch 112, an alarm lamp 113, and a thumb 114 for opening or closing the movable clamp 109 when the tube 105 is attached into or detached from the groove 110 are shown.
Such a foregoing device detects the dropping number of the medical liquid into the dropping tube 104 with the dropping sensor 106, calculates it into a dropping speed per unit time by a calculation device installed in the control device 107, moves a clamp 109 at constant speed so as to provide a predetermined dropping speed, and automatically controls a throttling amount of the tube 105.
However, since the liquid carrying control device only moves the clamp 109 at the constant speed for controlling the throttling amount of the tube 105, it is difficult to bring the dropping speed to a determined dropping number rapidly and stably when starting to send the liquid, despite resilience and recovery of the bendable tube 105. This will be explained with reference to FIG. 10.
FIG. 10 is a characteristic view showing the relationship between the throttling amount of the bendable tube 105 and the liquid dropping number, where A' - B' - C' and A" - B" - C" are S curves proper for two kinds of liquid sending sets, and A' and A" are landing points of 1st drops, and B' and B" are close to the determined values, and C' and C" are landing points of the maximum drops.
As is apparent from the same, with respect to the bendable tube 105 held between the stationary clamp 108 and the movable clamp 109, an opening area of the tube 105 is not proportional to the liquid flowing amount, and the dropping number is rapidly changed around A', A" and B', B" by slightly changing the throttling amount. Therefore, when the clamp 109 is moved at a certain speed, it is difficult to bring the throttling amount nearly to the determined value.
For example, if the movable clamp 109 is moved at the high speed for starting to send the liquid earlier, said changing of the dropping number exceeds a large range, and when the movable clamp 109 is returned at high sped to compensate for this exceeding, this return will overrun.
If the clamp 109 is moved at a determined high speed, it is difficult to converge the dropping number nearly to the determined values B', B", and the dropping number is made unstable.
If the clamp 109 is moved to the determined low speed for cancelling unstability, it takes much time (starting time for sending the liquid) to move the clamp 109 from a zero position (the position where the tube is completely closed) to the position of the first dropping.
Further, if the clamp 109 is moved at the determined middle speed, there occurs a defect involved with any one of the high speed movement and the low speed movement.
On the other hand, when the bendable tube 105 is attached to the control device 107 and since the tube 105 is inserted successively in the length of the narrow groove 110, the attachment is troublesome. Beside, the tube 105 is pressed in the groove 110 under pressure, so that the tube is loaded over a full length, and a portion about half way become twisted or caused with strain, and the medical liquid does not flow smoothly.